A11y for Dojo Mobile 1.8

Description

Currently there are no a11y checklist for mobile web applications. However Dojo Mobile would like to be as accessible as possible without sacrificing code size. The first step of this task is to define the scope of a11y support for mobile and then to implement the support appropriately.

Refs #14469 Added the closeIconRole and closeIconTitle properties to _IconItemPane. They can be used to give the 'role' and 'title' attributes to the close button through the iconItemPaneProps property of IconContainer?.

Refs #14469 !strict Keyboard navigation support for editable IconContainer?. test_IconContainer-editable-a11y.html was added to demonstrate how to make editable IconContainer? keyboard accessible. In this sample, you can enter the edit mode, and then put focus on an icon, and move it with Shift + Left/Right? keys, and delete it with the Delete key.